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MG MGA - 5 speed conversion

I've been thinking about my winter project to fit a Hi Gear 5 speed sierra box type 9 to my 1622 MGA MK2. The original diff was 4.1 to 1 but I've fitted a MGB diff of 3.9 to 1. I'm just checking to see if anyone has this combination and wondering if it would would make the gearing almost too high for the power output of the engine at say 4th and 5th gears? For a standard MGA with 4.3 to 1 diff the 3.9 to 1 is about 10% higher geared. This doesn't seem too much but you never know. Can one rely on the robustness of the sierra box or do they all have to be overhauled before use?
J H Cole


I have exactly that configuration. There is a thread down the page on the topic started by myself. The 3.9 gearing with the 1800 engine and Ford box will give you something like the following:

1000 rpm = 23.5 mph
1275 rpm = 30 mph
1700 rpm = 40 mph
2000 rpm = 47 mph
2125 rpm = 50 mph
2550 rpm = 60 mph
3000 rpm = 70.5 mph
3400 rpm = 80 mph
3800 rpm = 90 mph
4000 rpm = 94 mph
4250 rpm = 100 mph

Acceleration is excellent and no strain on the drive train as far as I have experienced. It took a week or two to get used to the different speeds for optimum gear changing, but no problem.

I love it.

Steve Gyles

I have just noticed that you are keeping the 1622 engine, so you will not have quite the power of the 1800 engine. But I would guess you will be okay as 3rd and 4th gears are very long and usable ratios.

I should also have added that there are a few other considerations including recalibrating the speedo. I would also recommend fitting a right angle speedo drive adapter to the gearbox. It cuts out speedo wander due to the otherwise bendy layout of the drive cable.

I found a box with about 30k on it. I did not touch it. Still going very strong after 6 years or so.

Steve Gyles

I have the 1622 in my MK2 but with the 4.1 rear end fitted the Sierra 5 speed last year with no problems ( I chickened out and got Peter Edney to fit the gearbox- my joints are getting too creaky to crawl under now !) Cruising at 75-80 @3500 revs. Speedy cables recalibrated my Speedo and did a super job
P D Camp

I have an 1800v engine, Sean Brown head, Hi gear 5 speed trans, Judson Supercharger 3.9 rear end. No problem with power and is a great freeway runner. The car will lack a little power because of the 3.9 but not a problem. The gearing is almost the same as the MGA. Only 2nd gear is a little higher. The 5th gear is 20% less rpm than a stock engine.

I made half a dozen calls to breakers yards in Hampshire and was surprised at the sparsity of the sierra gearbox. I can see that getting a used box let alone a low mileage one is going to be a problem. I know you can get renovated boxes but their quite a lot of money.
J H Cole

Hi all!
Somebody knows what will be the equivalent of the Ford Sierra Gearbox in USA?
R Garcia

An equivalent of the Ford Sierra in Canada was the Mercury Mercur. I don't know what they were marketted under in the US.
Fraser Cooper

Thank you, I think in US had the same model, but I will confirm. Regards.
R Garcia

Hi to J N Cole - the type 9 box is getting scarce, as you've discovered. Register with and yards will email you with availability and costs
A S Duff

> An equivalent of the Ford Sierra in Canada was the Mercury Mercur.

Check the archives for "Mercury Mercur". My understanding is several different Mercur models and engine/transmission combinations were used in North America. Only select models used a type 9 gearbox suitable for this application.
Andy Bounsall

I have a concern about future availability of these non OEM parts. When I did my MGA/RX7 conversion in 1987 I used a 5 year old drive train (1982) that was still in production. Now 20 years later any part is special order and will soon be discontinued. We keep our stuff for 25 plus years and as long as we take care of them they will last virtually forever. In todays market cars last 10 years and parts are discontinued after 15 20 max. The Mercur was never avaiable in very big numbers and it has been out of production for 10 years now.
R J Brown

RJ, I understand your concerns, but the Ford type 9 gearbox was used extensively throughout the model range in Europe and is the current gearbox of choice amongst many classic Ford motorsport enthusiasts, as well as the 5 speed conversions for other makes. The demand for spare parts for these gearboxes by far outweighs that for the MGA gearbox.

That said, times change and originality is always difficult to maintain. As greater numbers of cars are modified, the fewer original cars left are likely to become more desirable in years to come. Where possible I think it is a good idea to retain all those removed parts with the car, maybe the next trend will be restore cars back to original?
Neil McGurk

I have a 1600 MK I , the engine is stock, the drive train is a Hi -Gear 5 speed transmission with a 3.9 rear-end. Iím very happy with both the performance and the MPG (39) that I get from the car.
David werblow

I am considering intalling a ford type 5 gearbox and conversion as per the Hi-Gear kit. Really like the idea of dropping a few revs when cruising and having syncro on first --just looked at their site and kit is very comprehensive --even includes a short throw gear lever ( shift?). I've asked them the price for shipping here but think it is going to be revolting...does anyone know a company in Australia that imports such or makes a similar unit ?
neil ferguson

typos galore...meant to write 'installing a ford type 9 etc....'
neil ferguson

Couple of refurbished Type 9 boxes on Ebay: 110436346444

Steve Gyles

Hi Guys
Just popped in here while looking for other info for a customer and i'm glad i did ! As i am the man who recons the type 9's on Ebay Thanks for the mention Steve if i can help anyone drop me an email or give me a call 07966497815 (sensible hours please) lol !

First Motion Transmissions
Paul Mason

I have a warmed-up 1800, Ford 5-speed (which I love) and a 3.9. I do mostly So. Cal. freeway driving. I have come to conclude my preference would be, that combo, but with a 4.1. I could still cruse at 80, if I really wanted to, but with better around town performance.

Steve Meline
Steve Meline

This thread was discussed between 05/10/2009 and 19/10/2009

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